ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.37 2006/03/25 13:17:02 djm Exp $ */
   2 /*
   3  * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17 #include "includes.h"
  18
  19 #include <openssl/evp.h>
  20 #include <openssl/err.h>
  21
  22 #include "xmalloc.h"
  23 #include "log.h"
  24 #include "buffer.h"
  25 #include "bufaux.h"
  26 #include "key.h"
  27 #include "compat.h"
  28 #include "ssh.h"
  29
  30 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
  31
  32 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  33 int
  34 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
  35     const u_char *data, u_int datalen)
  36 {
  37         const EVP_MD *evp_md;
  38         EVP_MD_CTX md;
  39         u_char digest[EVP_MAX_MD_SIZE], *sig;
  40         u_int slen, dlen, len;
  41         int ok, nid;
  42         Buffer b;
  43
  44         if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
  45                 error("ssh_rsa_sign: no RSA key");
  46                 return -1;
  47         }
  48         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
  49         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
  50                 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
  51                 return -1;
  52         }
  53         EVP_DigestInit(&md, evp_md);
  54         EVP_DigestUpdate(&md, data, datalen);
  55         EVP_DigestFinal(&md, digest, &dlen);
  56
  57         slen = RSA_size(key->rsa);
  58         sig = xmalloc(slen);
  59
  60         ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
  61         memset(digest, 'd', sizeof(digest));
  62
  63         if (ok != 1) {
  64                 int ecode = ERR_get_error();
  65
  66                 error("ssh_rsa_sign: RSA_sign failed: %s",
  67                     ERR_error_string(ecode, NULL));
  68                 xfree(sig);
  69                 return -1;
  70         }
  71         if (len < slen) {
  72                 u_int diff = slen - len;
  73                 debug("slen %u > len %u", slen, len);
  74                 memmove(sig + diff, sig, len);
  75                 memset(sig, 0, diff);
  76         } else if (len > slen) {
  77                 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
  78                 xfree(sig);
  79                 return -1;
  80         }
  81         /* encode signature */
  82         buffer_init(&b);
  83         buffer_put_cstring(&b, "ssh-rsa");
  84         buffer_put_string(&b, sig, slen);
  85         len = buffer_len(&b);
  86         if (lenp != NULL)
  87                 *lenp = len;
  88         if (sigp != NULL) {
  89                 *sigp = xmalloc(len);
  90                 memcpy(*sigp, buffer_ptr(&b), len);
  91         }
  92         buffer_free(&b);
  93         memset(sig, 's', slen);
  94         xfree(sig);
  95
  96         return 0;
  97 }
  98
  99 int
 100 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 101     const u_char *data, u_int datalen)
 102 {
 103         Buffer b;
 104         const EVP_MD *evp_md;
 105         EVP_MD_CTX md;
 106         char *ktype;
 107         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 108         u_int len, dlen, modlen;
 109         int rlen, ret, nid;
 110
 111         if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) {
 112                 error("ssh_rsa_verify: no RSA key");
 113                 return -1;
 114         }
 115         if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 116                 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
 117                     BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
 118                 return -1;
 119         }
 120         buffer_init(&b);
 121         buffer_append(&b, signature, signaturelen);
 122         ktype = buffer_get_string(&b, NULL);
 123         if (strcmp("ssh-rsa", ktype) != 0) {
 124                 error("ssh_rsa_verify: cannot handle type %s", ktype);
 125                 buffer_free(&b);
 126                 xfree(ktype);
 127                 return -1;
 128         }
 129         xfree(ktype);
 130         sigblob = buffer_get_string(&b, &len);
 131         rlen = buffer_len(&b);
 132         buffer_free(&b);
 133         if (rlen != 0) {
 134                 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
 135                 xfree(sigblob);
 136                 return -1;
 137         }
 138         /* RSA_verify expects a signature of RSA_size */
 139         modlen = RSA_size(key->rsa);
 140         if (len > modlen) {
 141                 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
 142                 xfree(sigblob);
 143                 return -1;
 144         } else if (len < modlen) {
 145                 u_int diff = modlen - len;
 146                 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
 147                     modlen, len);
 148                 sigblob = xrealloc(sigblob, 1, modlen);
 149                 memmove(sigblob + diff, sigblob, len);
 150                 memset(sigblob, 0, diff);
 151                 len = modlen;
 152         }
 153         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
 154         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
 155                 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
 156                 xfree(sigblob);
 157                 return -1;
 158         }
 159         EVP_DigestInit(&md, evp_md);
 160         EVP_DigestUpdate(&md, data, datalen);
 161         EVP_DigestFinal(&md, digest, &dlen);
 162
 163         ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
 164         memset(digest, 'd', sizeof(digest));
 165         memset(sigblob, 's', len);
 166         xfree(sigblob);
 167         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
 168         return ret;
 169 }
 170
 171 /*
 172  * See:
 173  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 174  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 175  */
 176 /*
 177  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 178  *      oiw(14) secsig(3) algorithms(2) 26 }
 179  */
 180 static const u_char id_sha1[] = {
 181         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 182         0x30, 0x09, /* type Sequence, length 0x09 */
 183         0x06, 0x05, /* type OID, length 0x05 */
 184         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 185         0x05, 0x00, /* NULL */
 186         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 187 };
 188 /*
 189  * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 190  *      rsadsi(113549) digestAlgorithm(2) 5 }
 191  */
 192 static const u_char id_md5[] = {
 193         0x30, 0x20, /* type Sequence, length 0x20 (32) */
 194         0x30, 0x0c, /* type Sequence, length 0x09 */
 195         0x06, 0x08, /* type OID, length 0x05 */
 196         0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
 197         0x05, 0x00, /* NULL */
 198         0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
 199 };
 200
 201 static int
 202 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
 203     u_char *sigbuf, u_int siglen, RSA *rsa)
 204 {
 205         u_int ret, rsasize, oidlen = 0, hlen = 0;
 206         int len;
 207         const u_char *oid = NULL;
 208         u_char *decrypted = NULL;
 209
 210         ret = 0;
 211         switch (type) {
 212         case NID_sha1:
 213                 oid = id_sha1;
 214                 oidlen = sizeof(id_sha1);
 215                 hlen = 20;
 216                 break;
 217         case NID_md5:
 218                 oid = id_md5;
 219                 oidlen = sizeof(id_md5);
 220                 hlen = 16;
 221                 break;
 222         default:
 223                 goto done;
 224         }
 225         if (hashlen != hlen) {
 226                 error("bad hashlen");
 227                 goto done;
 228         }
 229         rsasize = RSA_size(rsa);
 230         if (siglen == 0 || siglen > rsasize) {
 231                 error("bad siglen");
 232                 goto done;
 233         }
 234         decrypted = xmalloc(rsasize);
 235         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 236             RSA_PKCS1_PADDING)) < 0) {
 237                 error("RSA_public_decrypt failed: %s",
 238                     ERR_error_string(ERR_get_error(), NULL));
 239                 goto done;
 240         }
 241         if (len < 0 || (u_int)len != hlen + oidlen) {
 242                 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
 243                 goto done;
 244         }
 245         if (memcmp(decrypted, oid, oidlen) != 0) {
 246                 error("oid mismatch");
 247                 goto done;
 248         }
 249         if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
 250                 error("hash mismatch");
 251                 goto done;
 252         }
 253         ret = 1;
 254 done:
 255         if (decrypted)
 256                 xfree(decrypted);
 257         return ret;
 258 }